Ammonium-nitrate explosive



Jan. 4,1927., 1,613,335

E. M. SYMMES AMMONIUM NI TRATE EXPLOS IVE Filed N'ov. 8, 1924 PatentedJan. `4, 1927.

UNITED STATES A 1,613,335 PATENT OFFICE.

ERNEST M. SYMMES, OEWILMINGTON, DELAWARE, ASSIGNOR TO HERCULES POWDERCOMPANY,.OF WILMINGTON, DELAWARE, A CORPORATION 0F DELAWARE.

ANTIMONIUM-NITRATE EXPLOSIVE.

The object of myinvention is to provide an ammonium nitrate explosivewhich is distinguished from ordinary ammonium' nitrate explosivesin`that it is less hygroscopic, more sensitive, much less dense, thusallowing a higher cartridge count, and which, as it passes through thetransition Apoint at 32 C., will n0t,,set up (harden) and so become sorelatively insensitive that it may not 'detonate properly.

The manufacture of my improved explosive is dependent on the use ofammonium nitrate having peculiar novel physical characteristics, and inorder to properly describe tlie production o'f explosives embodying thisinvention, it is necessary to describe the improved ammonium nitratewhich is a constituent of the explosive and the method of making it.

In the ordinary process of making ammonium nitrate, it is customary toprepare weak solutions of the salt and evaporate the solution to acertain concentration at a certain temperature,l after which thesolution is discharged into a gra'ining kettle and slowly crystallizedwith agitation and cooling at a certain rate. The rate ofcrystallization and concentration of the evaporated solution controlsthe fineness of the product. Slow crystallization of a highlyconcentratedlsolution produces coarse particles in the form of irregularbotryoidal solid crystals., Crystallizing at an increased rate resultsin relatively fine particles, which are also in the form of solidcrystals.

Granular ammonium nitrate produced by this process is composed of solidgrains, has greater density and hygroscopicity than is desirable, andwhen passing through the transition point at 32 C. (89.6 F.) there isconsiderable external expansion, which constitutes a serious objectionto explosives containinrT ammonium nitrate 11i substantial proportion,as the explosive sets (hardens) r as it passes through the transitionpoint and becomes relatively insensitive and may not vdetonate properly.y

The granular ammonium nitrate embodying the present invention issuperior to the productformed by'crystallizing a more or lessconcentrated solution in a graining kettle. As compared with theordinary product` it is milch less dense, thus allowing a highercartridge count in ammonium'nitrate permissible explosives; it is moresensitive; it is less hygroscopic; and in ypassing `through thetransition point at 32 C., there 1s less external expansion and ittherefore does not exhibit such a marked tendency to set up. i

It is certain thatsome of the above qualities, and it is possible thatall of them, ai'e due, in whole or in part, to the peculiar novelphysical characteristic exhibited by the granular ammonium nitrateembodying the present invention: namely, the granules or particles aresubstantially spherical inl form and have a hollow center. Such hollowspherical paiticles cannot be manufactured by the process in generaluse: namely, the crystallization in graining kettles with .agitation andcooling. On the other hand, their formation is not necessarily dependenton the use of any particular process and is certainly not dependent onthe use of any particular apparatus. i In order, however, that myimproved product may be produced by those skilled in the art, I shalldescribe a process of making it which has been found entirelysatisfactory as Well as operative. This process is set forth in acompanion application liled of even date herewith, Serial Number748,548. Itcomprises the projection of an evaporated solution ofammonium nitrate, through a nozzle or atomizer, at a substantiallydefinite pressure, into a gaseous cooling medium. An apparatus adaptedto carry out the process is shown in the accompanying drawing, which isa longitudinal sectional view of such apparatus.

A weak neutral ammonium nitrate liquor is concentrated in the evaporatora. From the evaporator the more or less concentrated solution, by meansof a pump 7), is conveyed through a steam-jacketed pipe c and dischargedthrough a nozzlel (l into the spray chamber e under suliioient pressureto elfcct the atomization of the solution. VIt should be understood thatthe term atoniization is used in its popular sense to imply a divisionofthe solution into a number of very line particles, which willsolidify' before they have traversedthe height of the spray chainber.The spray chamber is of substantial dimensions and is provided wili asloping bottom communicating with a hopper f which discharges thematerial into a rot-ating drying cylinder. g. From the drying cylinderthe dried material ,is discharged, say, onto a screen l1.; the gramswhich 1t 1s desired to utilize. as an explosive ingredient passingthrough the screen in to a receiver z', while the tailings pass overinto a separate receiver By means of a heater and a blower m, a currentof hot air or other gas is forced through thedrier, the air thenceescaping through the hopper f into the spray chamber e.

The character of the material produced by the improved process iscontrolled by the conditions under which the process is carried out. Ithas been found that the density of the material varies in asubstantiallydirect ratio to the freezing point, of the solution sprayed and in asubstantially inverse ratio to the temperature of the solution anddegree of atomization. In other words, the density of the productresulting from spraying a solution having a freezing polnt only slightlybelow the temperature of the solution when sprayed will be higher thanthat of the product from a solutionhaving the same freezing point butsprayed at a higher temperature. By controlling the freezin point andtemperature of the solution an the degree of atomization, the characterof the product'may be controlled. The freezing point of the solutionvaries with the degree of concentration. The degree of atomization maybe varied by varymg the pressure at the nozzle and to some extent byvarying the temperature of the solution when sprayed.

As an illustrationof the process, a weak solution of ammonium nitrate isconcentrated in the evaporator a to a point where the solution has atemperature of 310 F.

and at which the ammonium nitrate if taken out would freeze orerystallize at 280 F. With a steam pressure of fifty pounds to thesquare inch on the jacketed feed pipe c, thev solution is deliveredthrough the pump to the nozzle d at a pressure of twenty pounds to thesquare inch.

The heated air in chamber f may be at any desired temperature (say 100F. to 150 F and is substantially devoid of moisture. 'Ihis air, however,is very cold relatively to the incoming spray of ammonium nitrate, andalmost immediately cools the sprayed particles to the point ofsolidicaton. It will be understood that there is a continuous current ofdry air flowing into the bottom of chamber e and out the ventilators oat the lop thereof.

The ammonium nitrate is projected in the form of a vast number ofparticles of spherical form. From contact with the cooling gaseousmedium filling the spray chamber, these spheres quickly form an exteriorsolidified shell. The interior of each particle .freezes more slowlyand, due to the contraction that takes place on cooling, a void space isleft in the interior. The product has an apparent density of about .70andv a ineness (with the freezing point, temperature and degree ofatomization specified as an example) such that ninety-five per cent willpass through a ten mesh screen and be held on a forty mesh screen. Byincreasing the atomizing action, finer particles are produced. Forexample, the degree of fineness may be such that not more than five percent will be held on a forty mesh "screen, while five per cent or morewill pass through a hundred mesh screen, Whatever the degree offineness, the grains have a spherical form with an interior void space.Besides being muchless dense than granular ammonium nitrate produced bythe ordinary method, they are less hygroscopic and show less increase involume when passing through the 32 C. transition point.

The size and density of the material are both affected by, and may becontrolled by regulating, the freezing point, temperature and degree ofatomization of the liquid when sprayed. In all cases, however, thedensity will be low as compared with the ordinary product and there willbe a close approximation to uniformity in size. The density can beeasily varied from .6 to .9.

While the weak solution is described as being concentrated to a pointwhere the solution has a temperature of 310 F., crystallizing at 280 F.,it is contemplated that these temperatures shall be subject tovariation, dependent on the character or qualityl that it is desired toimpart to the' ultimate product. It is impracticable, however, 'to carryeither the crystallizlng temperature or the evaporating temperature muchhigher than 310 F., as decbmposition occurs in the neighborhood of 320F. The lowest practicable crystallizing temperature would be 250 F. orhigher. The temperature of the gas entering the spray chamber is imma--terial so long as it is substantially below the temperature of theliquid as it ,is being atomized. The gas should, of course, be nearlyfree from moisture. All required conditions can be .satisfied by usingair as the gaseous cooling medium and heating it to above 100 F. andbelow 150 F. I

The following are examples of ammonia permissible explosives embodyingmy invention, bearing in mind that the ammonium nitrate ingredient hasthe peculiar characteristics and qualities hereinbcfore descril'ied.

An anun'onia permissible explosive having the followmg typlcalcompositiom,

Percent. Nitroglycerin, nitropolyglycerin, nitrosugar, mtroglycol, orany other similar liquid explosive. y 10 Carbonaceous material 10Ammonium nitrate 80 Nitroaromatic compounds 3 Sodium nitrate 41Carbonaceous material 11 Ammonium nitrate 28 Ammonia gelatin (theexample given being low freezing) Per cem.. Any of the abovespeciiedliquid explosives Nitrocotton 0.6 Sodium nitrate 46.4 Sulphur3.0 Carbonaceous material 15.0 Ammonium nitrate 6.0

Having now' fully described my invention, what I claim and desire toprotect by Letters Patent is:

1. An explosive composition comprising a liquid explosive, carbonaceousmaterial and ammonium nitrate in the form of a multitude ofsubstantially spherical grains with internal cavities.

2. An explosive composition comprising a liquid explosive, carbonaceousmaterial and ammonium nitrate in the form of hollow granules having adensity between .6 and .9.

3. An explosive composition comprising a liquid explosive, carbonace `usmaterial and ammonium nitrate in the form of granules having an internalvoid space and having, as compared with ordinary commercial ammoniumnitrate, substantially lower density and less hygroscopicit and whichWill not substantially set or har en in passing through the transitionpoint at 32 C.

In testimony of which invention, I have hereunto set my hand, atWilmington, Del., on this 5th day of November, 1924.

ERNEST M. SYMMES.

